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Postfix Documentation
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Postfix ETRN Howto

Purpose of the Postfix fast ETRN service

The SMTP ETRN command was designed for sites that have intermittent Internet connectivity. With ETRN, a site can tell the mail server of its provider to "Please deliver all my mail now". The SMTP server searches the queue for mail to the customer, and delivers that mail by connecting to the customer's SMTP server. The mail is not delivered via the connection that was used for sending ETRN.

Postfix versions before 1.0 (also known as version 20010228) implemented the ETRN command in an inefficient manner: they simply attempted to deliver all queued mail. This is slow on mail servers that queue mail for many customers.

As of version 1.0, Postfix has a fast ETRN implementation that does not require Postfix to examine every queue file. Instead, Postfix maintains a record of what queue files contain mail for destinations that are configured for ETRN service. ETRN service is no longer available for domains that aren't configured for the service.

This document provides information on the following topics:

Other documents with information on this subject:

  • flush(8), flush service implementation
Postfix Documentation
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